The split promoter sequences of a tRNALeuCUG gene of Xenopus laevis have been mapped to nucleotides 13-20 and 51-64 of the tRNALeu coding sequences. The sequences closely coincide with two conserved sequence blocks present in all eukaryotic tRNA genes. The two conserved sequence blocks were found to be exchangeable between tRNA genes as chimaeric tRNAMet--tRNALeu genes proved transcriptionally active. Furthermore, two prokaryotic tRNA genes exhibiting strong homologies with the two blocks yielded specific transcripts when tested in an eukaryotic transcriptional system.
3′ Processing of sea urchin H3 histone pre‐mRNA depends on a small nuclear RNP which contains an RNA of nominally 60 nucleotide length, referred to below as U7 RNA. The U7 RNA can be enriched by precipitation of sea urchin U‐snRNPs with human systematic lupus erythematosus antiserum of the Sm serotype. We have prepared cDNA clones of U7 RNA and determined by hybridization techniques that this RNA is present in sea urchin eggs at 30‐fold lower molar concentration than U1 RNA. The RNA sequences derived from an analysis of eight U7 cDNA clones show neither homologies nor complementarities to any other know U‐RNAs. The 3′ portion of the presumptive RNA sequence can be folded into a stem‐loop structure. The 5′‐terminal sequences would be largely unstructured as free RNA. Their most striking feature is their base complementarity to the 3′ conserved sequences of histone pre‐mRNAs. Six out of nine bases of the conserved CAAGAAAGA sequence of the histone mRNA precursor and 13 out of 16 nucleotides from the conserved palindrome can be base paired with presumptive U7 RNA sequence, suggesting a unique hybrid structure for a processing intermediate formed from histone precursor and U7 RNA.
Re1at1ve p051t10n and 5tren9th5 0f p01y(A) 51te5 a5 we11 a5 tran5cr1pt10n term1nat10n are cr1t1ca1 t0 mem6rane ver5u5 5ecreted 1x-cha1n expre5510n dur1n9 8-ce11 deve10pment 6a6r1e11a 6a111,1 Jeffrey W. 6u15e, 2 M1chae1 A. McDev1tt, 1 Ph111p W. 7ucker, ~ and J05eph R. Nev1n51 1H0ward Hu9he5 Med1ca1 1n5t1tute, 7he R0ckefe11er Un1ver51ty, New Y0rk, New Y0rk 10021 U5A; 2Departrnent 0f M1cr0610109Y, 50uthwe5tern Med1ca1 5ch001, Un1ver51ty 0f 7exa5 Hea1th 5c1ence Center, Da11a5, 7exa5 75235 U5A Dur1n9 8-ce11 d1fferent1at10n, there 15 a dramat1c 5w1tch 1n the RNA pr0duct5 0f the 1mmun09106u11n ~ heavy cha1n tran5cr1pt10n un1t. 1n the mature 8 ce11 there 15 r0u9h1y e4ua1 pr0duct10n 0f the ~5 and the ~m RNA, wherea5 1n the ant160dy-5ecret1n9 p1a5ma ce11 there 15 near1y exc1u51ve pr0duct10n 0f the tx5 RNA. A p1a5m1d c0nta1n1n9 the ent1re ~ tran5cr1pt10n un1t wa5 pr0per1y re9u1ated when a55ayed 6y tran51ent tran5fect10n 1n a 8 1ymph0ma and a p1a5macyt0ma. 1n c0ntra5t, n0 5uch re9u1at10n wa5 065erved w1th 5eparate p1a5m1d5 that c0u1d pr0duce 0n1y 0ne 0r the 0ther RNA. 1n5tead, the ~m p01y(A) 51te wa5 ut1112ed m0re eff1c1ent1y than the tx5 p01y(A) 51te, 1rre5pect1ve 0f the ce11 type. We a150 f0und that tran5cr1pt10n term1nat10n pr10r t0 the ~m p01y(A) 51te 1n p1a5macyt0ma5 c0ntr16ute5 t0 preferent1a1 pr0duct10n 0f ~L5 RNA 1n the5e ce115. F1na11y, reduc1n9 the d15tance 6etween the tw0 p01y(A) 51te5 1mpr0ved the u5e 0f the ~m 51te at the expen5e 0f the u5e 0f the t~ 5 1n 8 1ymph0ma ce115, 5u99e5t1n9 a c0mpet1t10n f0r a 11m1t1n9 fact0r. 5uch c0mpet1t10n wa5 n0t apparent 1n p1a5macyt0ma5. We c0nc1ude that re1at1ve p01y(A) 51te 5tren9th and the p051t10n 0f the p01y(A) 51te5 w1th1n the tran5cr1pt10n un1t, c0up1ed w1th a chan91n9 c0ncentrat10n 0f a 11m1t1n9 fact0r, a5 we11 a5 tran5cr1pt10n term1nat10n pr10r t0 the ~m p01y(A) 51te, a11 p1ay a r01e 1n determ1n1n9 the expre5510n 0f the ~ 10cu5 dur1n9 8-ce11 deve10pment.[Key W0rd5: 19M; p01y(A) 51te ch01ce; tran5cr1pt10n term1nat10n] Rece1ved March 2, 1987; rev15ed ver510n accepted, May 8, 1987. Due t0 the c0mp1ex1ty 0f the pr0ce55 0f mRNA 610-9ene515 1n an an1ma1 ce11, the re9u1at10n 0f the 0utput 0f a 9ene can take many f0rm5 (Nev1n5 1983; 81rn5t1e1 et a1. 1985; Pad9ett et a1. 1986). 7h15 15 part1cu1ar1y true f0r c0mp1ex tran5cr1pt10n un1t5 that 9enerate mu1t1p1e mRNA pr0duct5.0ne 5uch examp1e 15 the 1mmun09106-u11n heavy-cha1n 10cu5. F0110w1n9 a55em61y 0f the var1-a61e re910n 9ene c0mp0nent5, the ~ heavy cha1n 0f 19M appear5 1n the cyt0p1a5m 0f pre-8 ce115. After 119ht-cha1n 9ene rearran9ement, 119ht cha1n5 and ~ heavy cha1n5 are a55em61ed 1nt0 19M, wh1ch 15 1ater c0-expre55ed 0n the ce11 mem6rane (m) w1th the c105e1y 11nked d0wn5tream 9ene pr0duct, 19D. 7he pre-8, 1mmature 8 (m19M +), and mature 8 (m19M + m19D +) ce115 have the capac1ty t0 pr0-duce tw0 f0rm5 0f the p. pr0te1n; a heavy cha1n that can 6e 5ecreted a5 an ant160dy m01ecu1e and a re1ated heavy cha1n that can 6e 1n5erted 1n the mem6rane a5 a recept0r f0r ant19en. When the mature 8 ce11 enc0unter5 ant19en, there 15 an ...
Alternative processing of the immunoglobulin mu primary transcript results in regulated production of mRNAs encoding the secreted (microseconds) and membrane-bound (micro m) form of IgM heavy chain during B-cell development. To elucidate the basis for this control, we analyzed the expression of altered forms of the mu transcription unit. Deletion of intron sequence between the microseconds and micro m exons, which reduces the distance between the two poly(A) sites as well as the distance between micro m splice sites, enhances production of micro m RNA. Correct expression is restored by insertion of heterologous sequences, demonstrating that spacing is indeed the critical aspect. The altered spacing appears to affect poly(A) site usage rather than splice site usage, since it was the distance between the poly(A) sites rather than the distance between splice sites that was found to be decisive. Finally, removal of either the C mu 4 splice donor or the m1 splice acceptor, thus eliminating normal micro m splicing, does not increase usage of the microseconds poly(A) site. We therefore conclude that the major factor in determining the ratio of microseconds to micro m is a poly(A) site choice rather than a splicing choice.
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